Electron tube amplification system



Patented Dec. 6, 1938 UNITED STATES PATENT FFICE Walter Soller, Tucson,Ariz., assigner of onehalf to William H. Woodin, Jr., Tucson, Ariz.

Application September 25, 1934, Serial No. 745,460v

2 Claims.

This application is a continuation in part of my application SerialNumber` 688,833 filed September 9, 1933 and entitled Balanced electrontube circuits.

One of the objects of my invention is to provide an electron tubeamplification system employing multiple electrode electron tubes inwhich the electrodes are interconnected by balanced circuits forinsuring stabilized operation of the ampliiication system.

Another object of my invention is to provide a balanced electron tubeampliiication system employing pentode electron tubes in which. al1stages are balanced for insuring stabilized operation of theamplification system.

Another object of my invention is to provide a circuit arrangement forinsuring balanced operation of a resistance coupled electron tubeampliiication system for eiecting maximum ampliiication per stagewithout interference from parasitic oscillations.

Still another object of my invention is to provide a resistance coupledelectron tube amplification system in which opposing potentials areintroduced in selected portions of the resistance coupled ampliercircuit for preventing oscillation while allowing maximum amplification.

Another object of my invention is to provide an electron tubeamplification system having circuits interconnecting the electrodes ofthe electron tubes including a resistor carrying current of one electrontube element, the potential drop across which is balanced by the sum ofa drop of potential across a resistor carrying part or all of thecurrent of the total supply power, and another voltage either producedby the drop in potential across a resistor carrying the current of' anyother element of the same tube or any separately introduced voltage ofany kind.

A further object of my invention is to provide an electron tubeampliiication system in which balanced operation is obtained bybalancing the potential drops in elements connected with the electrodesof the electron tubes to a substantially balanced condition and thenintroducing an additional voltage for completely balancing the operationof the amplification system.

A still further object of my invention is to provide a pentodeamplification system in which balancing of the entire ampliiier may beeliected in the final ampliiication stage.

Other and further objects of my invention reside in the method andcircuit arrangement for balancing the operation of electron tubesystems,- as set forth more fully in the specification hereinaiterfollowing by reference to the accompanying drawing, in which Figure 1 isa circuit arrangement of a pentode amplifier system employing myinvention; Figure 2 illustrates my invention as applied to a threeelement electron tube amplifier system and Figure 3 shows theapplication of my invention to a tetrode circuit wherein balancing isobtained in the iinal amplification stage.

Referring to the drawing in detail, Figure 1 illustrates my invention asapplied to a balanced amplifier employing pentode electron tubes. Any ofthe many multiple plate and grid tubes may be used in circuits similarto the circuit shown in Figure 1. In the arrangement shown in Figure ltwo stages of amplication have been. illustrated for the purpose ofexplaining my invention but it will be understood that any number ofamplication stages may be employed.

The pentodes are indicated by reference characters I. and 2. Pentode lincludes heater element la, cathode lb, grid electrodes lc, ld and leand plate electrode lf. Heater elementy la. is energized fromalternating current derived from a suitable power pack connected toterminals HH. Similarly, pentode 2 includes heater element 2a, cathode2b, grid electrodes 2c, 2d and 2e and plate electrode 2f. The inputcircuit to the ampliiier system is represented at 3; the output from theamplifier system is shown at 4. The power supply for each of thepentodes is secured by means of a series circuit adapted to be connectedto the filter system of a power rectiiier when the tubes are operatedfrom an alternating current source, or to the lter adapted forconnection to a direct current line circuit, or to a direct currentgenerator or a battery system.

The power supply circuit for each of. the pentodes comprises a'seriespath indicated generally at 5 containing resistors 6, l and 8. Theseresistors are selected in value to produce the desired potential dropfor supplying the required biasing potential to control grid Ic, thedesired potential to grid ld, the potential for grid le and also therequired potential for anode If. Grid le connects with cathode lb atpoint I3, which is in turn connected to a point intermediate resistors 6and 'l in the series path 5.

In addition to the resistors 6,1 and 8 in the series circuit I provideseparate potential determining resistors 9 and I0, disposed in seriesbetween the point II intermediate resistors 1 and 8 and the grid Id.Also I provide a resistor I2 connected at potential point I4 in theseries path 5 for determining the potential supplied to anode If. Theresistances are selected in such proportions that accurate balancedoperation of the amplier circuit is obtained. The succeeding pentode 2has the input circuit thereof connected with the output of pentode Ithrough connections shown at I5. The connection from control grid 2c ismade at a point I6 intermediate resistors 9 and I0 in circuit with gridId. The connection to the cathode 2b is taken at point Il in the outputcircuit of pentode I adjacent resistor I2 and adjacent the connection ofanode If thereto.

The resistance network and the connections to the electrodes in pentodeI, as above described, may be considered as a balanced bridgearrangement in which: resistance 8 constitutes one leg; resistance I2, asecond leg; the internal resistance between cathode Ib and anode I f ofthe tube, the third leg; and resistance 1, the fourth leg. This fourthleg is modified to include the internal resistance between the cathodeIb and the grid Id of the tube I and resistance elements S and Iiiconnected in series, the series circuit being connected in parallel withthe resistance 7. The source of potential for the bridge is connected atpoint I4 between resistances 8 and EZ'and to the cathode Ib. The outputis taken from the opposite terminals of the bridge, viz., IS and il. Themodication of the fourth leg of the bridge which includes resistance I@permits the resistance I0 to be included also in the output circuit. Thepotential drop across resistance Iii, or some equivalent voltage, is anecessary factor in the balancing of the bridge circuit.

The condition of balance of the bridge is the condition of zero Voltageacross the output terminals. Consider the voltage of cell 30 or thepotential drop across resistance It! as E, the re` sistances I2 and 8 asR1 and R0, respectively, and the currents in R1 and Ro as I1 and Io,respectively. The factors aifecting the balance of the bridge are thecurrents Io and I1. These currents are each dependent on a commonfactor, which is the source of potential of the system, and the eiectsthereof may be made to neutralize each other for any variations in thepotential source by properly adjusting the resistance of the circuit.

It will be appreciated that the same principles are involved in both adirect heated cathode circuitdevice, as shown in Fig. 2 and the indirectcathode heating system of Figs. 1 and 3 as long as all power is obtainedfrom the same source. There is a simultaneous change in the heating ofthe cathode andthe plate potential under conditions. of changes in thecommon power supply. Accordingly, variation in cathode emission due tovariation of power supply in the circuits of Figs. 1 and 3 will bebalanced similar to the direct heated system, as illustrated in Fig. 2.

The values of the two resistances R11 and R1 depend upon thecharacteristics of the tube and circuit. The simplest way to determinethis dependence is to regard the output circuit, the voltage E, and theresistances R0 and R1 as a Dowling zero shunt. When a current Io ispassing through R0 and the current I1 through R1, then the requirementfor no current through the output circuitis:

Now for the circuit to be balanced for a change AIO in Io and acorresponding change A11 in I1, the following equation must hold:

AI (3) -IO-I-IlA-Il 15 The above is the value of R0 for balancedconditions in terms of E, I1, Io and the slope'of the I1 Vs. Iocharacteristics. R1 is then determined by Equation 1. 20

If E is constant (E is a constant voltage cell 30 in Fig. 2 and in Figs.1 and 3, it can be considered as a first approximation as constant,because the Equation 5 is the general equation of a straight line.Therefore, if the portion of the characteristics near the operatingvalue of AIo is straight, the circuit will balance and remain balanced.

The length of this straight portion determines the range of externalfluctuations that can be balanced. This requirement is usually fullledfor normal operating conditions. Ihis one-tube circuit affords so simplea means of balancing external tube variations that it is as easily setup as an unbalanced circuit, will operate 'much more satisfactorily, andwith refinements, will balance as closely as the two-tube circuit. Theadvantages over the two-tube circuit are: the elimination of thediiiculty in balancing, of extra apparatus, and of the necessity ofobtaining exactly similar tubes, which are not readily procurable. Thebalancing in these circuits is accomplished by adjusting resistancesR11, R1, and voltage E; Without voltage E, the circuit wouldV notbalance even though it appears the' drop Ro, In could be made to balancedrop R1, I1. This is not possible, as can be seen, by allowing E toequal zero in the first equation after Equation 2, which willthen causeRoto cancel out of the equation and thereby eliminate the means ofadjusting for balance. To have an additional voltage E in the circuitRu, R1, 0 and the output, is an essential feature of these circuits, andmay be provided from a battery, a standard cell or the like, as in Fig.2, in lieu of the voltage drop across a resistance in the preferred formshown in Figs.. 1 and 3.

The actual values, of the resistances Ro and R1 need not be calculatedfrom Equations 3 and l, but can be determined experimentally as follows:A suitable D. C. electric current meter is .placed across the outputterminals with R not far from the expected correct value and R1 isadjusted until the meter reads zero. The supply current is thenincreased by increasing the voltage into the supply circuit and thedeilection of the meter noted. Then, with a new Value of R11 (a Valuewhich diers from the expected correct value in the opposite directionfrom that of the first Value taken), R1 is again adjusted for zeroreading of the meter, and the deflection of the meter again noted for anincrease in supply current. If the correct value of R0 for balance isnear the value which was expected, this second defiectionwill be in theopposite direction to the iirst. Values-of R0 between these two are thentaken and the above procedure repeated until a Value of Ro and R1 isfound for which no deflection is produced in the meter when the supplycurrent is changed. Every tube even of the same type and make differsenough in characteristics to require the values of Ro and R1 to bedetermined experimentally for balance against supply power changes.

The assumption that E is constant is introduced to simplify thediscussion and to show the fundamental idea of balancing against changesin supply power especially in the simplied'circuit of F'ig. 2, and alsoto sh'ow how closely the other circuits are related to it. Actually, theassumption of E being constant is an unnecessary assumption and can bereplaced by the assumption that the resistances I0, 8, and I2 remainconstant which can always be accurately fuliilled.

The following discussion will show that the circuits in Figs. l, 2, and3 will balance, not approximately, but completely for normal operatingvoltages on the tube and that the conditions are not altered from thosejust given, I!) being any suitable constant resistance, and R0 and R1Vdetermined experimentally in exactly the same way as before. Callresistance Ill, R2; and the current through it, I2. Then, for balance atsome current Io with the corresponding currents I1 and I2, the followingequation must hold:

NOW to remain balanced when In changes to Io-l-AID causing I2 to changeto Iz-j-Ai'z and I1 to I1+AI1, the following equation must hold also:

11H1- R212 Io Cancelling and rearranging, gives R1(I1.AI0 IgAIl)R2(I2AI0 I0'AI2) This is a similar condition to that of the previouscase, the denominator having exactly the same form. Here, the numeratoralso has exactly the same form. In order for the denominator to remainconstant with change of In and I1, it was shown that the onlyrequirement was that the I1-Io characteristics must be linear in theoperating region, so here in order that the numerator remains constantwith change of In and I2, the Iz--Io characteristics must also be linearin the operating region.V These two conditions are practically alwaysmet in amplifying tubes.

As it is the ratio RI RI R1: 11o-li; 22 (8) and then it is eliminated inplace of Ro, the second condition of balance,

AIO RLIVLKI A12 IVIIAI,

is obtained.

From this, it is seen that Ro can just as well be chosen arbitrarily inplace of R2 and then R2 and R1 adjusted for the balanced conditionexperimentally in exactly the same way as Ru and R1 were. This is a moreconvenient method of adjusting, as during adjustment, the tube can beheld closer to its operating voltages. As Ro is arbitrary, a specialcase of this circuit is when Rezo.

So far, it has been shown that these circuits will completely balanceout changes in the supply power sources. It will be shown now that afurther adjustment of the circuits in Figs. l, 2 and 3 is possible,whereby they will balance both changes in the power source, and changesin cathode emission due not only to variations in the power supply, butto any cause, as, for example, the deterioration of the cathode orlament. It is preferable to have the grid to which resistances 9 and Il]are connected, between the cathode and the control grid for this type ofbalancing. Let changes in the electron emission not due to power supplyvariations produce changes of AIz and AI1 in I2 and I1 respectively. Forthese changes, there will be no change in Io; i. e., AIO-:0. Forbalancing at currents Io, I1 and I2, we have R0I0+R2Ig=I1R1 OI'R0=I`1R1R2I2 Then for balance after a change AIz and A'Ir when I0 doesnot change,

Equations 8, 9, and 10 are the three conditions that must be fulfilledfor this balance` Let the slopes A I0 LIL A11-10' Mini N12-n' Then bysubstituting these values in Equations 8, 9, and 10 and eliminating theRs we obtain the condition between the currents and slopes that must befullled. The circuit of Fig. 3 fullflls all the requirements of Fig. 1in that one. power supply source is used and further allows balancingthe entire cascade at the output ofthe nal tube.

A series power supply circuit is provided. for pentode 2 similar tothepower supply. circuit in the rst pentode stage. I have indicated theseries power supply circuit for pentode 2 by reference character 5'. Inthe series circuit 5' there are resistor elements corresponding to thoselocated in the power supply circuit 'of pentode I, that is, theresistors 6', 1' and 8'. Grid 2e connects to cathode 2b at point I3',which in turn connects to a potential point intermediate resistors 6'and 1' in series path/5. The grid electrode 2d is maintained at apre-determined. potential through a connection which includes resistors9 and I Il', which connection is taken from point I I intermediateresistors 1 and 8' in the power supply circuit 5'. Anode 2 f ismaintained at the required potential by a connection through resistorI2' to I4' in the series path 5'. The output circuit 4 connects betweenterminal I6 intermediate resistors 9'and IIJ and terminal I1' in theoutput circuit of pentode 2. The resistors are selected for such valueas to obtain accurate balanced operation of the pentode stages.

Referring to Figure 2 of the drawing I have shown the balanced circuitof my invention applied to a three electrode electron tube amplier. Inthis arrangement the three electrode electron tubes are indicated at I8and I9. Tube I8. includes cathode. lila, control grid Ib and anode |80.Tube I9 includes cathode lila, control grid I9b and anode |90. The inputcircuit is shown at 20. The output circuit connects at ZI. A directcurrent source, such as the output terminals of a filter connected Witha direct current generator, the output of the power pack of a rectierunit or a battery source is connected with terminals 22. The seriescircuit 23 is arranged similarly to the series circuit 5 in Figure l,which circuit includes resistors 24, 25 and 25 connected in seriesthrough the cathode I8a.

The potential supplied to anode i8c is determined by resistor 21connected at the point 28 in the series path 23 and adjacent theresistor 25'. The desired operating potential on grid Ib obtained byconnection of the grid circuit to the point 29 in the series path 23.The succeeding three electrode tube I9 has its input circuitconnectedwith the output circuit of three electrode tube I8 in a very specialmanner designed to produce the same results which are eiTective whenusing pentodes as illustrated in the circuit of Figure 1. That is tosay, an additional balancing voltage is introduced into the couplingcircuit between tube !9 and tube I8. This is accomplished in the circuitof Figure 2 by employing the cell 30, having its positive terminalconnected to the point SI intermediate resistors 25 and 25 in seriespath 23 and having its negative terminal connected to control grid I9b.This additionalcell replaces the drop which is obtained in the resistors9 and I9 of the circuit of Figure 1 and which connect with grid Id.

In applying the equations above to the circuits in Fig. 2, the voltageof cell 30 is represented by E, and resistances 21 and 26 by R1 and R0,respectively.

The circuit of my invention, either in the form shown in Figure 1 or inFigure 2', provides means for balancing the power current change againstthe plate current change. Balancing the potential drops due to the powercurrent change and the plate current change is not s'uicient. Anadditional and separate voltage must VAbe introducedintothe circuit. InFigure 21this additional voltage isV introducedv by means of a cell31|;` in Figure 1 this additional voltageis introduced by the potentialdrop across resistors. 9 and. III. in circuit withl grid Id. Balancedoperation of the electron tube circuits is thereby. assured. The inputcircuit of tube I9, connected as aforesaid from control grid I9b to theadditional potential source 30, has its input circuit completed by theconnection from point 29 tothe terminal 32 intermediate the end ofresistor 21 and anode IBc.

The power supply for the` succeeding electron tube I9 is provided in amanner similar tothe power supply for tube I 8inseries path 23",connected with terminals 22', theseries pathY containing resistors 24',25' and 26' connected` in series through cathode I9a. Resistor 24provides a drop which is combined withl the drops produced by resistors21' and 26' andY combined with the potential of source 30 to stabilizethe potential on control grid |91). Anode |90 is provided with requiredpotential through the drop across resistor 21'. The output circuit tothe next succeeding electron tube, which connects the terminals 2|, isconnected through they additional source of potential 30' forintroducing the balancing voltage as heretofore explained.

My invention is applicable to circuits employing electron tubes ofvarious. constructions, such as screen grid tubes, pentodes andmulti-electrode tubes employing a plurality of grid and plateelectrodes, and according to the type of tube employed I may provide a`cell to` introduce the desired potential drop for balancing or I mayderive the balancing potential from the drop across resistors in circuitwith a grid electrode as heretofore described in connection with-Figure 1. Where structural conditions permit I may combine the powersupply circuits ofv ay multiplicity of electron tubes, as shown inFigure 3.

In this arrangement tubes 33 and 34 are shown with the output circuit ofone tube coupled with the input circuit ofthe succeeding tube and havingan input circuit and an output circuit 36. The power supply of directcurrent characteristic is connected at, 31 and traversesY the seriespath 38, which path contains resistors 39, 40,- 4I, 42, 43 and 44. Tube33 includes heater element 33a, cathode 33b, grid 33e, grid 33d andplate 33e. Similarly, electron tube 3 4 contains heater element 34a,cathode 34h, grid 34e, grid 34d and plate 34e.

The grid bias potential for tube 33 is determinedr by theV drop across.resistor 39v which is disposed in the grid cathode circuit. The potenvtial on grid 33d is determined by the drop across resistor 4D. The anodepotential for-anodev 33e is determined by the drop across resistors 40and 4I. The output circuit olftube 33 is coupled with the input circuitof tube 34 through resistor 45. The bias on control grid 34o isdetermined by the drop across resistor 42. The potential on grid 34d isderived` from the drop across resistor 43. The balancing potential ongrid 34d is determined by the drop4 across resistors 46 and 41 connectedin series with tap 48 intermediate resistors 43 and 44. The potential onanode 34e is determined by resistor 49 connected with point 50 in theseries power supply circuit 38. The output circuit of the amplier at 35connects at point 5I intermediate resistors 46 and 41 in circuit withgrid 34d and the point 52 in the Output circuit of tube 34. In applyingthe equation above to the balancing circuit in Fig. 3, the voltage dropacross resistance 41 is represented byv E,

and resistances 49 and 44, by R1 and Ro, respectively.

All of the stages of the amplifier illustrated in Fig. 3 are balanced inthe last stage. This is possible because a common power supply circuitis provided for all of the stages. It will be noted that in the circuitsof Figs. 1 and 2 separate power supply paths are provided for eachstage.

My invention is directed to any method of changing the characteristicsof a tube, as for example, by placing a resistance across the tube, sothat it can be balanced. My invention is not confined to electron tubes,but is applicable to any form of cathode ray tubes.

My invention contemplates any amplification system of one or moreelectron tubes having three or more elements in which all elements ofeach tube are supplied by one source of electric power and in which thedrop in potential across a resistor carrying the current of one elementcan be balanced by the sum of a drop of potential across a resistorcarrying part or all of the total supply power current and anothervoltage either produced by the drop in potential across a resistorcarrying the current of any other element of the same tube or anyseparately introduced voltage of any kind.

I have described my invention in certain preferred embodiments but Idesire that it be understood that modications may be made withoutdeparting from the spirit of my invention. For example, I have mentionedthe arrangement of resistors in the power supply paths. I may employimpedances in the power supply paths in lieu of resistors. Other changesmay be made in the circuits of my invention and I intend no limitationsupon my invention other than imposed by the scope of the appendedclaims.

What I claim and desire to secure by Letters Patent of the United Statesis as follows:

1. An amplification system comprising a multiplicity of electron tubes,each including a cathode, a control grid and an anode, a separate seriescircuit containing a source of potential for energizing said cathode andanode in each of said electron tubes, a connection including a resistorfrom one terminal of said source of potential to said anode, aconnection from the series circuit connected with the succeedingelectron tube to the anode of the preceding electron tube, a connectionfrom the control grid of the succeeding electron tube to a point in theseries circuit connected with the preceding electron tube thence througha resistor in said series circuit to the terminal of said source ofpotential connected with said anode, and a source of compensatingpotential included in said last mentioned con nection for balancing thepotential across the connections to the succeeding electron tubecircuits.

2. An electron tube amplification system including a plurality ofelectron tube devices each having anode, cathode and grid electrodes, asource of power individual to each of said electron tube devices,circuits interconnecting the electrodes in each electron tube device andthe corresponding source of power comprising a connection from oneterminal of said source of power to the anode electrode, a resistanceelement in said connection, a series circuit including a plurality ofresistance elements connected to said source of power, a connection fromsaid cathode electrode to a point in said series circuit intermediatetwo of said plurality of resistance elements, output terminals, one ofsaid output terminals connected to said anode, and a separate source ofpotential, the other of said output terminals connected through saidseparate source of potential to a point in said series circuit thencethrough another of said plurality of resistance elements to the terminalof said source of power connected to said anode, the potentials of saidoutput terminals being balanced by the algebraic sum of the voltageacross said separate source of potential and the potential drops acrossthe resistance element connected between said separate source ofpotential and said source of power, and across the resistance elementconnected between said anode and said source of power, the anode outputterminal of a preceding electron tube device being connected throughanother of the plurality of resistance elements in the series circuitconnected with the succeeding electron tube device to the cathode ofsaid succeeding electron tube device, and the other of the outputterminals being connected with the grid electrode in said succeedingelectron tube device.

WALTER SOLLER.

